AT&T, the exclusive carrier for iPhone in the U.S., announced today that it will support auto-authentication for iPhone OS 3.0 users connecting to AT&T Wi-Fi Hotspots. Auto-authentication support means that iPhone users can potentially switch seamlessly from AT&T's 3G network to an AT&T Wi-Fi hotspot without taking any action.

Before, iPhone users had to go through a two-step authentication process in order to connect to AT&T's Wi-Fi. With the new method, auto-connect is established after the user connects her iPhone to an AT&T Wi-Fi hotspot for the first time.

Currently, AT&T operates roughly 20,000 U.S. hotspots at airports, coffee shops, including Starbucks, and other retail outlets, such as Barnes & Noble booksellers, as well as at McDonald's restaurants. In order to get access to them, subscribers must have a qualifying iPhone data plan--or they can pay $3.99 for temporary access. In a statement issued today, AT&T said in just the first quarter of 2009, more than four million connections were made at its U.S. hotspots with smartphones, including the iPhone 3G.

The new auto-authentication process is available starting today to all existing iPhone and iPhone 3G customers who download the free iPhone OS 3.0 software update via iTunes. It will also be available to all iPhone 3G S customers once that product goes on sale Friday. Meanwhile, all iPhone customers can continue to get AT&T Wi-Fi access with the current authentication process.